Translation of metal-phthalocyanines adsorbed on Au(111): from van der Waals interaction to strong electronic correlation

Boosting the Electrocatalytic Conversion of Nitrogen to Ammonia on Metal-Phthalocyanine-Based Two-Dimensional Conjugated Covalent Organic Frameworks

The electrochemical N₂ reduction reaction (NRR) under ambient conditions is attractive in replacing the current Haber-Bosch process toward sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising NRR electrocatalysts. However, simultaneously boosting their NRR activity and selectivity remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M-N₄-C centers as novel, defined, and effective catalysts, achieving simultaneously enhanced activity and selectivity of electrocatalytic NRR to ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn, and Cu) and pyrene units bonded by pyrazine linkages. Significantly, the 2D c-COFs with Fe-N₄-C center exhibit higher ammonia yield rate (33.6 μg h^-1 mg_cat^-1) and Faradaic efficiency (FE, 31.9%) at -0.1 V vs reversible hydrogen electrode than those with other M-N₄-C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h^-1 mg_cat^-1 and FE > 30%). In situ X-ray absorption spectroscopy, Raman spectroelectrochemistry, and theoretical calculations unveil that Fe-N₄-C centers act as catalytic sites. They show a unique electronic structure with localized electronic states at Fermi level, allowing for stronger interaction with N₂ and thus faster N₂ activation and NRR kinetics than other M-N₄-C centers. Our work opens the possibility of developing metal-nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalyst and provides an atomic understanding of the NRR process on M-N_x-C based electrocatalysts for designing high-performance NRR catalysts.

Temperature-Independent Polarization of Ultrathin Phthalocyanine-Based Hybrid Organic/Inorganic Heterojunctions

The combination of organic and inorganic materials at the nanoscale to form functional hybrid structures is a powerful strategy to develop novel electronic devices. The knowledge on semiconductor thin-film polarization brings direct benefits to the hybrid organic/inorganic electronics, becoming primordial for the development of devices such as electromechanical logic gates, solar cells, miniaturized valves, organic diodes, and molecular supercapacitors, among others. Here, we report on the dielectric polarization of ultrathin organic semiconducting films-ca. 5 nm thick metal phthalocyanine ensembles (viz., CuPc, CoPc, F16CuPc)-employed to build up hybrid metal/oxide/molecule heterojunctions. Such hybrid heterostructures are fully integrated into self-rolled nanomembrane-based capacitors and further investigated by impedance spectroscopy measurements as a function of temperature (from 6 to 300 K). The dielectric polarization of the metal phthalocyanines is found to be thermally activated above a specific threshold temperature, which depends on the molecular structure. Below this threshold, the current leakage across the system is suppressed, thus evidencing intrinsic-like polarization mechanisms. The temperature-independent permittivities of the ultrathin molecular films are found to be strongly dependent on the organic/inorganic hybrid interfaces, while the calculated relaxation times are more likely related to each single-molecule polarization. Beyond the advances in determining the temperature dependence of the permittivity for ultrathin phthalocyanine films integrated within solid-state electronics, our results also support the deterministic design of novel functional devices based on nanoscale hybrid organic/inorganic heterojunctions.

Screening nature of the van der Waals density functional method: a review and analysis of the many-body physics foundation

We review the screening nature and many-body physics foundation of the van der Waals density functional (vdW-DF) method [Berland Ket al2015Rep. Prog. Phys.78066501], a systematic approach to construct truly nonlocal exchange-correlation energy density functionals. To that end we define and focus on a class of consistent vdW-DF versions that adhere to the Lindhard screening logic of the full method formulation. The consistent-exchange vdW-DF-cx version [Berland K and Hyldgaard P 2014Phys. Rev. B89035412] and its spin extension [Thonhauser Tet al2015Phys. Rev. Lett.115136402] represent the first examples of this class; in general, consistent vdW-DFs reflect a concerted expansion of a formal recast of the adiabatic-connection formula [Hyldgaard Pet al2014Phys. Rev. B90075148], an exponential summation of contributions to the local-field response, and the Dyson equation. We argue that the screening emphasis is essential because the exchange-correlation energy reflects an effective electrodynamics set by a long-range interaction. Two consequences are that (1) there are, in principle, no wiggle room in how one balances exchange and correlation, for example, in vdW-DF-cx, and that (2) consistent vdW-DFs have a formal structure that allows them to incorporate vertex-correction effects, at least in the case of levels that experience recoil-less interactions (for example, near the Fermi surface). We explore the extent to which the strictly nonempirical vdW-DF-cx formulation can serve as a systematic extension of the constraint-based semilocal functionals. For validation, we provide a complete survey of vdW-DF-cx performance for broad molecular processes, for the full set of 55 benchmarks in GMTKN55 [Goerigk Let al2017Phys. Chem. Chem. Phys.1932184] and comparing to the quantum-chemistry calculations that are summarized in that paper. We also provide new vdW-DF-cx results for metal surface energies and work functions that we compare to experiment. Finally, we use the screening insight to separate the vdW-DF nonlocal-correlation term into pure-vdW-interaction and local-field-susceptibility effects and present tools to compute and map the binding signatures.

The effect of translation on the binding energy for transition-metal porphyrines adsorbed on Ag(111) surface

The characteristics of interaction between six transition-metal porphyrines and the Ag(111) surface are detailed here as resulted from DFT calculations. Van der Waals interactions as well as the strong correlation in 3d orbitals of transition metals were taken into account in all calculations, including the structural relaxation. For each system we investigate four relative positions of the metallic atom on top the surface. We show that the interaction between the transition metal and silver is the result of a combination between the dispersion interaction, charge transfer and weak chemical interaction. The detailed analysis of the physical properties, such as dipolar and magnetic moments and the molecule-surface charge transfer, analyzed for different geometric configurations allows us to propose qualitative models, relevant for the understanding of the self-assembly processes and related phenomena.